1. Field of the Invention
The subject of the invention relates to an Optical Fibre Connector, and more particularly to the ferrule which holds the optical fibre.
2. Description of the Prior Art
Optical fibre connectors are typically comprised of a fibre core coaxially positioned in a ferrule, which is then retained in an outer housing or sleeve. Generally, a latching mechanism retains two fibers or a fibre and an electronic component in electrical engagement. Typical examples include a bayonet style ring, or a plastic outer housing having a resilient latching system.
The composition of a ferrule is typically chosen depending on the application for which the fibre connectors are used, and more particularly by the optical quality of the system. For example, for a system requiring high return loss, the ferrule is typically comprised of ceramic or metal, but in other systems for example in automotive sensors where a low return loss is adequate, the ferrules can be comprised of a plastic molded ferrule. In any event, the optical quality of the system is a function of the axial alignment of the fibre ends as well as how well the fibre ends butt together.
With reference to FIG. 1, a well known prior art system is shown schematically where two ferrules having a chamfered leading edge is provided and where the end face of the ferrule is flat, that is perpendicular to the axial direction. The fibres would be located in an aperture along the centerline of the ferrules such that when the two ferrules butt together, the two fibre end faces are also butted one against the other. In a system such as that shown in FIG. 1, where the ferrules are comprised of a ceramic material, it is common to place the fibre within the ferrule, adhesively fix the fibre within the ferrule and grind the end face to provide a smooth polished surface. This provides the best butting engagement between the end faces as well as provides a highly polished fibre face to prevent light loss.
With reference now to FIG. 2, a later prior art system is shown where two ferrules are shown having a radiused end face, again where a fibre would be inserted within an aperture of the ferrule, wherein the convex surface at the end race provided precision abutment of the two ferrules along the centerline of the ferrules. This type of system prevents the two ferrules from butting together at any other location than at the axial centerline where the fibres are.
With respect now to FIG. 3, it is also known to offset the end face of the ferrule by an angle .alpha. where this angle is usually between 7.degree.-15.degree.. The reasoning behind such an angled offset is to improve the return loss in the fibre system. While the offset has improved the return loss, a further problem is caused when the ferrule also requires a chamfered outer edge.
As the surface is polished, the vertex of the convex surface CS is transferred to a position V as best shown in FIG. 3 while the centerline of the fibre end face remains along the centerline of the ferrule at F. Such ferrules and fibres are polished by pressing the ferrule and fibre together against a grinding medium such that the ferrule and fibre are held at an angle relative to the grinding medium, thereby causing the offset angle. The problem results in that, when grinding, the high point of the convex surface is located at the vertex. This is due to the fact that the polishing medium "finds" its own center, and that center is the geometric center of the convex surface. Theoretically, if two ferrules could be polished identically, the two would butt together at the centerline of the ferrules.
However, in practice, the difficulty occurs in that no two ferrules can be polished identically the same, such that in one case a ferrule may be polished as shown in FIG. 3, while the next ferrule is polished as shown in FIG. 4. It should be noted that the ferrule of FIG. 3 is polished further down than that of FIG. 4. The more material that is taken off the end face of the ferrule, the further the vertex of the convex surface formed is offset, such that d1 in FIG. 3 is greater than d2 in FIG. 4. While these distances are small, when these two ferrules are butted one against the other, as shown in FIG. 5 the ferrules do not butt together at the centerline of the fibres, but rather at a position offset from the centerline of the fibres as shown in the exploded view of FIG. 5 causing separation of the fibre end faces by a distance "x".
U.S. Pat. No. 5,140,660 to Seiko Giken addresses this common problem, and in an attempt to solve this problem, configures a ferrule with a front cylindrical tip extending forward from the remainder of the body portion of the ferrule. The chamfered section is located on the main body portion and the only portion which is ground to a convex surface at an offset angle is the very tip portion. While this system overcomes the problem of the ferrules being mis-matched as shown in FIG. 5, the portion of the fibre extending forward in the tip of the ferrule is unsupported by the associated alignment sleeve, and could itself lead to fibre misalignment.